Lochlan is my husband's favorite name for a girl. To me it does not scream boy or girl so I could see it used for either. I like it but it's not my favorite. I like the idea of using Lo as a nickname. The only person with the name I know in real life is a girl who spells it Locklynn so to me it is more of a girl name than boy name.

Hmm, what are the first two children named? It'd help in recommending more names. Most of the names you listed ended in the -on sound even if they aren't spelled that way, so I'll suggest mostly similar sounding ones. I don't really like Locklin on a girl, sorry. It has the trendy -lin ending a lot of girls names have nowadays, but I find the Lock sound in the first syllable too masculine.